The present invention is that of a combination which achieves in a unitary device various flow-regulating effects in an oxygen-supply system, primarily that of a system for medical use in an oxygen-therapy program for a patient, although other utilization may also be served, in the dispensing of gas dispensing from a cryogenic liquid storage system.
More particularly, the present invention provides a combination of concepts which in their combination achieve both an automatic venting and non-venting, according to the patient's usage of oxygen at any particular time, automatically providing both safety-venting but also economical non-venting according to the patient's usage of the gaseous oxygen from the liquified oxygen storage reservoir, yet also providing a regulated flow to the patient to conform to a maximum flow-rate prescribed as maximum for the patient yet also permitting a downward adjustment of the flow-rate by the patient; and, regardless of the patient's adjustment of the flow rate, the safety venting or economical non-venting acts automatically according to that usage and to the gas evaporation as heat enters the cryogenic liquid supply reservoir.
The nature and effects of the invention of the novel combination here achieved can perhaps be easiest understood by a summary of problems or factors of a cryogenic supply system, particularly that of dispensing of oxygen (in gaseous state, of course) to a patient undergoing a therapy in which oxygen is being administered. Some of the factors are already quite apparent, but they are included anyway, as having an effect on the overall accomplishments achieved by the novel combination, especially since from the prior art basic components of the combination are here not only conceded as used but are emphasized:
1. The storage of the oxygen is in an extremely cold (cryogenic) liquid state.
2. Ambient heat entering the storage reservoir causes a continuing boil-off or evaporation (often called the Normal Evaporation Rate, or simple "NER") of the stored oxygen.
3. The oxygen from the storage reservoir is used by the patient in a gaseous state, and given additional warming from that of the temperature of the gaseous oxygen in the reservoir zone (called the "ullage") of the oxygen gas above the liquid oxygen in the storage reservoir.
4. The NER is constantly present, even though it changes somewhat in magnitude according to such factors as room-heat (ambient temperature), proportion of the reservoir container having liquid oxygen in contrast to the ullage region, added warm-up to the gaseous oxygen in the dispensing lines, etc.
5. The patient's demand for oxygen is not always constant, due to differences in activity or other matters of the patient's real or imagined needs, this factor having become increasingly important in recent years due to more "at home" patient-care in contrast to hospitalization of oxygen-therapy patients, yielding several aspects of non-constancy of patient-demand in comparison to the sedentary and continually-uniform (relatively at least) conditions of a hospital.
6. The "plumbing" or hardware, both rigid and flexible, of oxygen-supply systems is, for both economy and low-weight especially in "walk-around" systems, relatively light in weight and strength; and thus any non-used increase of gas pressure, as caused inevitably by the NER, can cause danger to the system and even to the patient, if not safely vented, quite desirably automatic.
7. Patients seem to be prone to a desire to give themselves an over-supply of oxygen if the supply is not effectively maximized; and this has long been realized as a danger of oxygen therapy, such a danger that for years physicians would require hospitalization for oxygen-therapy to minimize change of overdose.
8. The expense of oxygen, and the limitation of patient-freedom as caused by a need of conservation of the liquid oxygen supply and need of replenishment of the stored oxygen reserve, give a corresponding desire that the safety venting be automatically stopped when not needed for safety.
9. Automaticness and foolproofness of all the flow-regulation incidentals, as to all of the factors indicated in the above summary, as well as a desire for minimal maintenance, are particularly important, for patient well-being, economy of oxygen, and economy of the equipment.